1. Field of the Invention
The present invention relates to a pressurized clamp or chuck for clamping or securing tools or workpieces, and in particular for axially securing tools or workpieces mounted on a shaft, for example grinding wheels, milling tools, or the like; the clamp has a floating circular piston which is mounted at the front of the device and is adjustable axially by means of a pressurized fluid.
2. Description of the Prior Art
Existing clamps of this type are used to secure the workpiece or tool, for example between a stop and a nut bolted to the end of a shaft The circular device is thereby located between the workpiece or the tool, and the nut. In some designs, the clamp is provided with a female or inside thread so that it can be screwed directly onto the relevant shaft end. There are also other types in which the clamp is fitted with an external or male thread, for example for screwing into a hollow cylinder.
The clamping process is effected by pressing the floating piston axially against the workpiece, since it can move along the axis of the shaft. Thus, for example, the piston can be connected hydrostatically to one or more tangentially or axially arranged adjustment pistons via channels inside the clamp. When the adjustment piston is pressed in, the main piston is pressed out beyond the fixed front surface of the device, whereby the necessary power is transmitted due to the fact that the active area of the adjustment piston is much smaller than that of the main piston. An externally accessible screw is provided for pushing in the adjustment piston; this screw is located axially or coaxially to the adjustment piston. For securing or clamping, the device is screwed onto the shaft end by hand until it is pressed against the workpiece or tool. The securing screws of the adjustment piston are then screwed in with a tool, for example a key, until the pressure produced by the adJustment pistons and the hydraulic fluid is sufficient for the clamping power required, which can be read off an indicator.
There are also types in which the hydrostatic pressure required for extending the main piston is applied by pressure pins, rings, or a grease gun.
The drawback of the heretofore known clamps is that the piston does not return automatically to its initial position when the pressure is released, for example during dismantling of the clamp. After every clamping process, the piston must be pressed back into the clamp unit. In practice, this is often achieved by screwing the clamp further onto the shaft, after the hydrostatic pressure has been released, until the piston has returned to its initial position In order to do this, sometimes more power is required than that normally available by hand, so that this work could only be carried out with other tools, such as key wrenches or hook spanners. This is time-consuming on the one hand, and on the other hand there is a risk of damaging the clamp.
An object of the present invention is to provide a clamp such that the piston is reset automatically when the hydrostatic pressure within the clamp is released.